Network Working Group C. Daboo
Internet-Draft Apple
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vCard Extensions to WebDAV (CardDAV)draft-daboo-carddav-04
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Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract
This document defines extensions to the Web Distributed Authoring and
Versioning (WebDAV) protocol to specify a standard way of accessing,
managing, and sharing contact information based on the vCard format.
Discussion of this Internet-Draft is taking place on the mailing list
<http://lists.osafoundation.org/mailman/listinfo/ietf-carddav>.
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Internet-Draft vCard Extensions to WebDAV (CardDAV) February 20081. Introduction and Overview
Address books containing contact information are a key component of
personal information management tools, such as email, calendaring and
scheduling, and instant messaging clients. To date several protocols
have been used for remote access to contact data, including
Lightweight Directory Access Protocol LDAP [RFC2251], Internet
Message Support Protocol IMSP [IMSP] and Application Configuration
Access Protocol ACAP [RFC2244], together with SyncML used for
synchronization of such data.
1.1. IMSP
IMSP [IMSP], which was the predecessor to ACAP [RFC2244], received
limited support from vendors, but those that did implement solutions
based on it, found it to be a useful feature for large deployments of
email clients at sites where users may roam from machine to machine.
IMSP provided for multiple personal, shared or public address books,
organized in a hierarchy, and gave individual users the ability to
control access to their address books so that they could grant read
or write access rights to other specific users or groups. This
provided an easy and convenient way for users or workgroups to
quickly setup and manage shared address information. Address book
support in IMSP suffers from a number of problems, including a
limited format for the address data itself, and scalability issues
with large address books.
The key features of address book support in IMSP are:
1. Ability to use multiple address books with hierarchical layout.
2. Ability to control access to individual address books.
3. Server-side searching of address data, avoiding the need for
clients to download an entire address book in order to do a quick
address 'expansion' operation.
4. Ability to download/upload an individual address in an address
book.
The key disadvantages of address book support in IMSP are:
1. Limited schema for address data.
2. Does not scale to large address books (e.g. no way to page
through the list of addresses in an address book).
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3. Does not provide any type of synchronization capability, which
easily leads to 'lost update' problems when multiple users are
editing the same address book entries.
4. Lack of internationalization support.
5. Does not provide per-address access control.
6. Does not provide a simple way to lookup users on the system.
1.2. ACAP
ACAP [RFC2244] was meant as the successor to IMSP and as such was
designed to be a more 'generic' data access protocol for general
application use. ACAP defined specific 'datasets' (basically formal
schema definitions) for different anticipated areas of use, including
address books, email accounts, application preferences, mime types
etc. The use of such formal schema definitions was intended to
enhance interoperability between clients. However, ACAP proved
difficult to implement due to over complexity in the protocol itself,
and this lead to few implementations.
The key features of address book support in ACAP are:
1. Ability to use multiple address books with hierarchical layout.
2. Ability to control access to individual address books and
address entries.
3. Server-side searching of address data, avoiding the need for
clients to download an entire address book in order to do a
quick address 'expansion' operation.
4. Ability to inherit address book data from others.
5. Ability to watch changes in address book data through use of
'contexts'.
6. Ability to page through address book data through use of
'contexts'.
7. Internationalization support through use of UTF-8 for all data.
8. Well defined address schema to enhance client interoperability.
9. Compatibility with vCard data format.
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10. Users and groups dataset can be used to enumerate and find other
users on the system.
The key disadvantages of address book support in ACAP are:
1. Inheritance, access control and contexts all together is hard,
and ultimately proved one of the major hurdles to
implementations.
1.3. LDAP
LDAP [RFC2251] is a generic directory access protocol that is
specifically targeted at management applications and browser
applications that provide read/write interactive access to
directories. Often such directories contain information about
people, including contact/address data.
The key features of address book support in LDAP are:
1. To do.
The key disadvantages of address book support in LDAP are:
1. Lack of schemas require overly complex client configuration to
map expected fields in the client to directory entries in the
server.
2. General reluctance to give 'ordinary' users write access to even
a small portion of the directory as often sensitive information
is included in directory entries and a small mistake in
configuring access control can lead to a major security breach.
1.4. SyncML
SyncML is a protocol for synchronizing data, including contacts,
between different devices.
More...
1.5. WebDAV for Address Books
WebDAV [RFC4918] offers a number of advantages as a framework or
basis for address book access and management. Most of these
advantages boil down to a significant reduction in design costs,
implementation costs, interoperability test costs and deployment
costs.
The key features of address book support with WebDAV are:
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1. Ability to use multiple address books with hierarchical layout.
2. Ability to control access to individual address books and address
entries.
3. Principal namespace can be used to enumerate and find other users
on the system.
4. Server-side searching of address data, avoiding the need for
clients to download an entire address book in order to do a quick
address 'expansion' operation.
5. Well-defined internationalization support through standard HTTP.
6. Use of vCards for well defined address schema to enhance client
interoperability.
7. Many limited clients (e.g. mobile devices) contain an HTTP stack
which makes implementing WebDAV much easier than other protocols.
The key disadvantages of address book support in WebDAV are:
1. Lack of change notification.
2. Stateless nature of protocol can result in more data being sent
with each transaction to maintain per-user session across
requests.
1.6. vCard
vCard [RFC2426] is a MIME directory profile aimed at encapsulating
personal addressing and contact information about people. The
specification of vCard was originally done by the Versit consortium,
with a subsequent 3.0 version standardized by the IETF [RFC2426].
vCard is in wide spread use in email clients and mobile devices as a
means of encapsulating address information for transport via email,
or for import/export and synchronization operations.
2. Conventions2.1. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The term "protected" is used in the Conformance field of property
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definitions as defined in Section 15 of [RFC4918].
When XML element types in the namespaces "DAV:" and
"urn:ietf:params:xml:ns:carddav" are referenced in this document
outside of the context of an XML fragment, the string "DAV:" and
"CARDDAV:" will be prefixed to the element type names, respectively.
2.2. XML Namespaces and Processing
Definitions of XML elements in this document use XML element type
declarations (as found in XML Document Type Declarations), described
in Section 3.2 of [W3C.REC-xml-20060816].
The namespace "urn:ietf:params:xml:ns:carddav" is reserved for the
XML elements defined in this specification, its revisions, and
related CardDAV specifications. XML elements defined by individual
implementations MUST NOT use the "urn:ietf:params:xml:ns:carddav"
namespace, and instead should use a namespace that they control.
The XML declarations used in this document do not include namespace
information. Thus, implementers must not use these declarations as
the only way to create valid CardDAV properties or to validate
CardDAV XML element type. Some of the declarations refer to XML
elements defined by WebDAV [RFC4918] which use the "DAV:" namespace.
Wherever such XML elements appear, they are explicitly prefixed with
"DAV:" to avoid confusion.
Also note that some CardDAV XML element names are identical to WebDAV
XML element names, though their namespace differs. Care must be
taken not to confuse the two sets of names.
Processing of XML by CardDAV clients and servers MUST follow the
rules described in Appendix A of [RFC4918].
3. Requirements Overview
This section lists what functionality is required of a CardDAV
server. To advertise support for CardDAV, a server:
o MUST support vCard [RFC2426] as a media type for the address
object resource format;
o MUST support WebDAV Class 3 [RFC4918];
o MUST support WebDAV ACL [RFC3744];
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o MUST support secure transport as defined in [RFC2818] using TLS
v1.0 [RFC2246] or a subsequent standards-track version of TLS;
o MUST support ETags [RFC2616] with additional requirements
specified in Section 6.3.2.3 of this document;
o MUST support all address book REPORTs defined in Section 8 of this
document; and
o MUST advertise support on all addressbook collections and address
object resources for the addressbook reports in the DAV:supported-
report-set property, as defined in Versioning Extensions to WebDAV
[RFC3253].
In addition, a server:
o SHOULD support the extended MKCOL method
[draft-daboo-webdav-mkcol-00] to create address book collections
as defined in Section 6.3.1 of this document.
4. Address Book Data Model
As a brief overview, a CardDAV address book is modeled as a WebDAV
collection with a well defined structure; each of these address book
collections contain a number of resources representing address
objects as their direct child resources. Each resource representing
an address object is called an "address object resource". Each
address object resource and each address book collection can be
individually locked and have individual WebDAV properties.
Requirements derived from this model are provided in Section 5.1 and
Section 5.2.
4.1. Address Book Server
A CardDAV server is an address-aware engine combined with a WebDAV
server. The server may include address data in some parts of its URL
namespace, and non-address data in other parts.
A WebDAV server can advertise itself as a CardDAV server if it
supports the functionality defined in this specification at any point
within the root of its repository. That might mean that address data
is spread throughout the repository and mixed with non-address data
in nearby collections (e.g. address data may be found in /lisa/
addressbook/ as well as in /bernard/addressbook/, and non-address
data in /lisa/calendars/). Or, it might mean that address data can
be found only in certain sections of the repository (e.g.
/addressbooks/user/). Address book features are only required in the
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repository sections that are or contain address objects. So a
repository confining address data to the /carddav/ collection would
only need to support the CardDAV required features within that
collection.
The CardDAV server is the canonical location for address data and
state information. Clients may submit requests to change data or
download data. Clients may store address objects offline and attempt
to synchronize at a later time. However, clients MUST be prepared
for address data on the server to change between the time of last
synchronization and when attempting an update, as address book
collections may be shared and accessible via multiple clients.
Entity tags and other features help this work.
5. Address Book Resources5.1. Address Object Resources
This specification uses vCard as the default format for address or
contact information being stored on the server. However, this
specification does allow other formats for address data provided that
the server advertises support for those additional formats as
described below. The requirements in this section pertain to vCard
address data, or formats that follow the semantics of vCard data.
Address object resources contained in address book collections MUST
contain a single vCard component only.
vCard components in an address book collection MUST have a UID
property value that MUST be unique in the scope of the address book
collection in which it is contained.
5.2. Address Book Collections
Address book collections appear to clients as a WebDAV collection
resource, identified by a URL. An address book collection MUST
report the DAV:collection and CARDDAV:addressbook XML elements in the
value of the DAV:resourcetype property. The element type declaration
for CARDDAV:addressbook is:
<!ELEMENT addressbook EMPTY>
An address book collection can be created through provisioning (e.g.,
automatically created when a user's account is provisioned), or it
can be created with the extended MKCOL method (see Section 6.3.1).
This can be used by a user to create additional address books (e.g.,
"soccer team members") or for users to share an address book (e.g.,
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"sales team contacts"). Note however that this document doesn't
define what extra address book collections are for. Users must rely
on non-standard cues to find out what an address book collection is
for, or use the CARDDAV:addressbook-description property defined in
Section 6.2.1 to provide such a cue.
The following restrictions are applied to the resources within an
address book collection:
a. Address book collections MUST only contain address object
resources and collections that are not address book collections.
i.e., the only "top-level" non-collection resources allowed in an
address book collection are address object resources. This
ensures that address book clients do not have to deal with non-
address data in an address book collection, though they do have
to distinguish between address object resources and collections
when using standard WebDAV techniques to examine the contents of
a collection.
b. Collections contained in address book collections MUST NOT
contain address book collections at any depth. i.e., "nesting" of
address book collections within other address book collections at
any depth is not allowed. This specification does not define how
collections contained in an address book collection are used or
how they relate to any address object resources contained in the
address book collection.
Multiple address book collections MAY be children of the same
collection.
6. Address Book Feature6.1. Address Book Support
A server supporting the features described in this document, MUST
include "addressbook" as a field in the DAV response header from an
OPTIONS request on any resource that supports any address book
properties, reports, or methods. A value of "addressbook" in the DAV
response header MUST indicate that the server supports all MUST level
requirements and REQUIRED features specified in this document.
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>> Request <<
OPTIONS /addressbooks/users/ HTTP/1.1
Host: addressbook.example.com
>> Response <<
HTTP/1.1 200 OK
Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
Allow: MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, REPORT, ACL
DAV: 1, 2, 3, access-control, addressbook
DAV: extended-mkcol
Date: Sat, 11 Nov 2006 09:32:12 GMT
Content-Length: 0
In this example, the OPTIONS response indicates that the server
supports CardDAV in this namespace, therefore the '/addressbooks/
users/' collection may be used as a parent for address book
collections as the extended MKCOL method is available, and as a
possible target for REPORT requests for address book reports.
6.2. Address Book Properties6.2.1. CARDDAV:addressbook-description Property
Name: addressbook-description
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Provides a human-readable description of the address book
collection.
Value: Any text.
Protected: SHOULD NOT be protected so that users can specify a
description.
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
allprop behavior: SHOULD be returned by a PROPFIND DAV:allprop
request.
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Description: This property contains a description of the address
book collection that is suitable for presentation to a user.
Definition:
<!ELEMENT addressbook-description (#PCDATA)>
<!-- PCDATA value: string -->
Example:
<C:addressbook-description xml:lang="fr-CA"
xmlns:C="urn:ietf:params:xml:ns:carddav"
>Adresses de Oliver Daboo</C:addressbook-description>
6.2.2. CARDDAV:supported-address-data Property
Name: supported-address-data
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Specifies what media types are allowed for address object
resources in an address book collection.
Protected: MUST be protected as it indicates the level of support
provided by the server.
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
allprop behavior: SHOULD be returned by a PROPFIND DAV:allprop
request.
Description: The CARDDAV:supported-address-data property is used to
specify the media type supported for the address object resources
contained in a given address book collection (e.g., vCard version
3.0). Any attempt by the client to store address object resources
with a media type not listed in this property MUST result in an
error, with the CARDDAV:supported-address-data precondition
(Section 6.3.2.1) being violated. In the absence of this property
the server MUST only accept data with the media type "text/vcard"
and vCard version 3.0, and clients can assume that.
Definition:
<!ELEMENT supported-address-data (address-data+)>
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Example:
<C:supported-address-data
xmlns:C="urn:ietf:params:xml:ns:carddav">
<C:address-data content-type="text/vcard" version="3.0"/>
</C:supported-address-data>
6.2.3. CARDDAV:max-resource-size Property
Name: max-resource-size
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Provides a numeric value indicating the maximum size of a
resource in octets that the server is willing to accept when an
address object resource is stored in an address book collection.
Value: Any text representing a numeric value.
Protected: MUST be protected as it indicates limits provided by the
server.
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
allprop behavior: SHOULD be returned by a PROPFIND DAV:allprop
request.
Description: The CARDDAV:max-resource-size is used to specify a
numeric value that represents the maximum size in octets that the
server is willing to accept when an address object resource is
stored in an address book collection. Any attempt to store an
address book object resource exceeding this size MUST result in an
error, with the CARDDAV:max-resource-size precondition
(Section 6.3.2.1) being violated. In the absence of this property
the client can assume that the server will allow storing a
resource of any reasonable size.
Definition:
<!ELEMENT max-resource-size (#PCDATA)>
<!-- PCDATA value: a numeric value (positive integer) -->
Example:
<C:max-resource-size xmlns:C="urn:ietf:params:xml:ns:carddav"
>102400</C:max-resource-size>
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Internet-Draft vCard Extensions to WebDAV (CardDAV) February 20086.3. Creating Resources
Address book collections and address object resources may be created
by either a CardDAV client or by the CardDAV server. This
specification defines restrictions and a data model that both clients
and servers MUST adhere to when manipulating such address data.
6.3.1. Extended MKCOL Method
An HTTP request using the extended MKCOL method
[draft-daboo-webdav-mkcol-00] can be used to create a new address
book collection resource. A server MAY restrict address book
collection creation to particular collections.
To create an address book, the client sends an extended MKCOL request
to the server and in the body of the request sets the DAV:
resourcetype property to the resource type for an address book
collection as defined in Section 5.2.
Support for creating address books on the server is only RECOMMENDED
and not REQUIRED because some address book stores only support one
address book per user (or principal), and those are typically pre-
created for each account. However, servers and clients are strongly
encouraged to support address book creation whenever possible to
allow users to create multiple address book collections to help
organize their data better.
Clients SHOULD use the DAV:displayname property for a human-readable
name of the address book. Clients can either specify the value of
the DAV:displayname property in the request body of the extended
MKCOL request, or alternatively issue a PROPPATCH request to change
the DAV:displayname property to the appropriate value immediately
after using the extended MKCOL request. Clients SHOULD NOT set the
DAV: displayname property to be the same as any other address book
collection at the same URI "level". When displaying address book
collections to users, clients SHOULD check the DAV:displayname
property and use that value as the name of the address book. In the
event that the DAV: displayname property is not set, the client MAY
use the last part of the address book collection URI as the name,
however that path segment may be "opaque" and not represent any
meaningful human-readable text.
6.3.1.1. Example - Successful MKCOL request
This example creates an address book collection called /home/lisa/
addressbook/ on the server addressbook.example.com with specific
values for the properties DAV:resourcetype, DAV:displayname and
CARDDAV:addressbook-description.
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Clients populate address book collections with address object
resources. The URL for each address object resource is entirely
arbitrary, and does not need to bear a specific relationship (but
might) to the address object resource's vCard properties or other
metadata. New address object resources MUST be created with a PUT
request targeted at an unmapped URI. A PUT request targeted at a
mapped URI updates an existing address object resource.
When servers create new resources, it's not hard for the server to
choose a unique URL. It's slightly tougher for clients, because a
client might not want to examine all resources in the collection, and
might not want to lock the entire collection to ensure that a new one
isn't created with a name collision. However, there is an HTTP
feature to mitigate this. If the client intends to create a new
address resource the client SHOULD use the HTTP header "If-None-
Match: *" on the PUT request. The Request-URI on the PUT request
MUST include the target collection, where the resource is to be
created, plus the name of the resource in the last path segment. The
"If-None-Match" header ensures that the client will not inadvertently
overwrite an existing resource even, if the last path segment turned
out to already be used.
>> Request <<
PUT /lisa/addressbook/newvcard.vcf HTTP/1.1
If-None-Match: *
Host: addressbook.example.com
Content-Type: text/vcard
Content-Length: xxx
BEGIN:VCARD
VERSION:3.0
FN:Cyrus Daboo
N:Daboo;Cyrus
ADR;TYPE=POSTAL:;2822 Email HQ;Suite 2821;RFCVille;PA;15213;USA
EMAIL;TYPE=INTERNET,PREF:cyrus@example.com
NICKNAME:me
NOTE:Example VCard.
ORG:Self Employed
TEL;TYPE=WORK,VOICE:412 605 0499
TEL;TYPE=FAX:412 605 0705
URL:http://www.example.com
UID:1234-5678-9000-1
END:VCARD
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>> Response <<
HTTP/1.1 201 Created
Date: Thu, 02 Sep 2004 16:53:32 GMT
Content-Length: 0
ETag: "123456789-000-111"
The request to change an existing address object resource is the
same, but with a specific ETag in the "If-Match" header, rather than
the "If-None-Match" header.
File names for vCards are commonly suffixed by ".vcf", and clients
may choose to use the same convention for URLs.
6.3.2.1. Additional Preconditions for PUT, COPY and MOVE
This specification creates additional Preconditions for PUT, COPY and
MOVE methods. These preconditions apply:
o When a PUT operation of an address object resource into an address
book collection occurs.
o When a COPY or MOVE operation of an address object resource into
an address book collection occurs.
The new preconditions are:
(CARDDAV:supported-address-data): The resource submitted in the
PUT request, or targeted by a COPY or MOVE request MUST be a
supported media type (i.e., vCard) for address object resources;
(CARDDAV:valid-address-data): The resource submitted in the PUT
request, or targeted by a COPY or MOVE request MUST be valid data
for the media type being specified (i.e., MUST contain valid vCard
data);
(CARDDAV:no-uid-conflict): The resource submitted in the PUT
request, or targeted by a COPY or MOVE request MUST NOT specify a
vCard UID property value already in use in the targeted address
book collection or overwrite an existing address object resource
with one that has a different UID property value. Servers SHOULD
report the URL of the resource that is already making use of the
same UID property value in the DAV:href element;
<!ELEMENT no-uid-conflict (DAV:href)>
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(CARDDAV:addressbook-collection-location-ok): In a COPY or MOVE
request, when the Request-URI is an address book collection, the
URI targeted by the Destination HTTP Request header MUST identify
a location where an address book collection can be created;
(CARDDAV:max-resource-size): The resource submitted in the PUT
request, or targeted by a COPY or MOVE request MUST have an octet
size less than or equal to the value of the CARDDAV:max-resource-
size property value (Section 6.2.3) on the address book collection
where the resource will be stored;
6.3.2.2. Non-Standard vCard Properties, and Parameters
vCard provides a "standard mechanism for doing non-standard things".
This extension support allows implementers to make use of non-
standard properties and parameters whose names are prefixed with the
text "X-".
Servers MUST support the use of non-standard properties and
parameters in address object resources stored via the PUT method.
Servers may need to enforce rules for their own "private" properties
or parameters, so servers MAY reject any attempt by the client to
change those or use values for those outside of any restrictions the
server may have. Servers SHOULD ensure that any "private" properties
or parameters it uses follow the convention of including a vendor id
in the "X-" name, as described in Section 3.8 of [RFC2426], e.g.,
"X-ABC-PRIVATE".
6.3.2.3. Address Object Resource Entity Tag
The DAV:getetag property MUST be defined and set to a strong entity
tag on all address object resources.
A response to a GET request targeted at an address object resource
MUST contain an ETag response header field indicating the current
value of the strong entity tag of the address object resource.
Servers SHOULD return a strong entity tag (ETag header) in a PUT
response when the stored address object resource is equivalent by
octet equality to the address object resource submitted in the body
of the PUT request. This allows clients to reliably use the returned
strong entity tag for data synchronization purposes. For instance,
the client can do a PROPFIND request on the stored address object
resource and have the DAV:getetag property returned, and compare that
value with the strong entity tag it received on the PUT response, and
know that if they are equal, then the address object resource on the
server has not been changed.
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In the case where the data stored by a server as a result of a PUT
request is not equivalent by octet equality to the submitted address
object resource, the behavior of the ETag response header is not
specified here, with the exception that a strong entity tag MUST NOT
be returned in the response. As a result, clients may need to
retrieve the modified address object resource (and ETag) as a basis
for further changes, rather than use the address object resource it
had sent with the PUT request.
7. Address Book Access Control
CardDAV servers MUST support and adhere to the requirements of WebDAV
ACL [RFC3744]. WebDAV ACL provides a framework for an extensible set
of privileges that can be applied to WebDAV collections and ordinary
resources.
7.1. Additional Principal Properties
This section defines additional properties for WebDAV principal
resources as defined in [RFC3744].
7.1.1. CARDDAV:addressbook-home-set Property
Name: addressbook-home-set
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Identifies the URL of any WebDAV collections that contain
address book collections owned by the associated principal
resource.
Protected: MAY be protected if the server has fixed locations in
which address books are created.
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
allprop behavior: SHOULD be returned by a PROPFIND DAV:allprop
request.
Description: The CARDDAV:addressbook-home-set property is meant to
allow users to easily find the address book collections owned by
the principal. Typically, users will group all the address book
collections that they own under a common collection. This
property specifies the URL of collections that either are address
book collections or ordinary collections that have child or
descendant address book collections owned by the principal.
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This section defines the reports that CardDAV servers MUST support on
address book collections and address object resources.
CardDAV servers MUST advertise support for these REPORTs on all
address book collections and address object resources with the DAV:
supported-report-set property defined in Section 3.1.5 of [RFC3253].
CardDAV servers MAY also advertise support for these REPORTs on
ordinary collections.
Some of these REPORTs allow address data (from possibly multiple
resources) to be returned.
8.1. REPORT Method
The REPORT method (defined in Section 3.6 of [RFC3253]) provides an
extensible mechanism for obtaining information about a resource.
Unlike the PROPFIND method, which returns the value of one or more
named properties, the REPORT method can involve more complex
processing. REPORT is valuable in cases where the server has access
to all of the information needed to perform the complex request (such
as a query), and where it would require multiple requests for the
client to retrieve the information needed to perform the same
request.
A server that supports this specification MUST support the DAV:
expand-property report (defined in Section 3.8 of [RFC3253]).
8.2. Ordinary collections
Servers MAY support the REPORTs defined in this document on ordinary
collections (collections that are not address book collections) in
addition to address book collections or address object resources. In
computing responses to the REPORTs on ordinary collections, servers
MUST only consider address object resources contained in address book
collections that are targeted by the REPORT based on the value of the
Depth request header.
8.3. Searching Text: Collations
Some of the reports defined in this section do text matches of
character strings provided by the client and compared to stored
address data. Since vCard data is by default encoded in the UTF-8
charset and may include characters outside of the US-ASCII charset
range in some property and parameter values, there is a need to
ensure that text matching follows well-defined rules.
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To deal with this, this specification makes use of the IANA Collation
Registry defined in [RFC4790] to specify collations that may be used
to carry out the text comparison operations with a well-defined rule.
Collations supported by the server MUST support "equality" and
"substring" match operations as per [RFC4790] Section 4.2, including
the "prefix" and "suffix" options for "substring" matching. CardDAV
uses these match options for "equals", "contains", "starts-with" and
"ends-with" match operations.
CardDAV servers are REQUIRED to support the "i;ascii-casemap"
[RFC4790] and "i;unicode-casemap" [RFC5051] collations, and MAY
support other collations.
Servers MUST advertise the set of collations that they support via
the CARDDAV:supported-collation-set property defined on any resource
that supports reports that use collations.
In the absence of a collation explicitly specified by the client, or
if the client specifies the "default" collation identifier (as
defined in [RFC4790] Section 3.1), the server MUST default to using
"i;unicode-casemap" as the collation.
Wildcards (as defined in [RFC4790] Section 3.2) MUST NOT be used in
the collation identifier.
If the client chooses a collation not supported by the server, the
server MUST respond with a CARDDAV:supported-collation precondition
error response.
8.3.1. CARDDAV:supported-collation-set Property
Name: supported-collation-set
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Identifies the set of collations supported by the server
for text matching operations.
Protected: MUST be protected as it indicates support provided by the
server.
COPY/MOVE behavior: This property value MUST be preserved in COPY
and MOVE operations.
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allprop behavior: SHOULD be returned by a PROPFIND DAV:allprop
request.
Description: The CARDDAV:supported-collation-set property contains
zero or more CARDDAV:supported-collation elements which specify
the collection identifiers of the collations supported by the
server.
Definition:
<!ELEMENT supported-collation-set (supported-collation*)>
<!ELEMENT supported-collation (#PCDATA)>
Example:
<C:supported-collation-set
xmlns:C="urn:ietf:params:xml:ns:carddav">
<C:supported-collation>i;ascii-casemap</C:supported-collation>
<C:supported-collation>i;octet</C:supported-collation>
<C:supported-collation>i;unicode-casemap</C:supported-collation>
</C:supported-collation-set>
8.4. Partial Retrieval
Some address book REPORTs defined in this document allow partial
retrieval of address object resources. A CardDAV client can specify
what information to return in the body of an address book REPORT
request.
A CardDAV client can request particular WebDAV property values, all
WebDAV property values, or a list of the names of the resource's
WebDAV properties. A CardDAV client can also request address data to
be returned and whether all vCard properties should be returned or
only particular ones. See CARDDAV:address-data in Section 10.4.
8.5. Non-standard properties and parameters
Servers MUST support the use of non-standard property or parameter
names in the CARDDAV:address-data XML element in address book REPORT
requests to allow clients to request that non-standard properties and
parameters be returned in the address data provided in the response.
Servers MAY support the use of non-standard property or parameter
names in the CARDDAV:prop-filter and CARDDAV:param-filter XML
elements specified in the CARDDAV:filter XML element of address book
REPORT requests.
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Servers MUST fail with the CARDDAV:supported-filter precondition if
an address book REPORT request uses a CARDDAV:prop-filter or CARDDAV:
param-filter XML element that makes reference to a non-standard
property or parameter name which the server does not support queries
on.
8.6. CARDDAV:addressbook-query Report
The CARDDAV:addressbook-query REPORT performs a search for all
address object resources that match a specified filter. The response
of this REPORT will contain all the WebDAV properties and address
object resource data specified in the request. In the case of the
CARDDAV:address-data XML element, one can explicitly specify the
vCard properties that should be returned in the address object
resource data that matches the filter.
The format of this report is modeled on the PROPFIND method. The
request and response bodies of the CARDAV:addressbook-query report
use XML elements that are also used by PROPFIND. In particular the
request can include XML elements to request WebDAV properties to be
returned. When that occurs the response should follow the same
behavior as PROPFIND with respect to the DAV:multistatus response
elements used to return specific property results. For instance, a
request to retrieve the value of a property which does not exist is
an error and MUST be noted with a response XML element which contains
a 404 (Not Found) status value.
Support for the CARDDAV:addressbook-query REPORT is REQUIRED.
Marshalling:
The request body MUST be a CARDDAV:addressbook-query XML element
as defined in Section 10.3.
The request MAY include a Depth header. If no Depth header is
included, Depth:0 is assumed.
The response body for a successful request MUST be a DAV:
multistatus XML element (i.e., the response uses the same format
as the response for PROPFIND). In the case where there are no
response elements, the returned DAV:multistatus XML element is
empty.
The response body for a successful CARDDAV:addressbook-query
REPORT request MUST contain a DAV:response element for each
address object that matched the search filter. address data is
returned in the CARDDAV:address-data XML element inside the DAV:
propstat XML element.
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Preconditions:
(CARDDAV:supported-address-data): The attributes "content-type"
and "version" of the CARDDAV:address-data XML element (see
Section 10.4) specify a media type supported by the server for
address object resources.
(CARDDAV:supported-filter): The CARDDAV:prop-filter (see
Section 10.5.1) and CARDDAV:param-filter (see Section 10.5.2) XML
elements used in the CARDDAV:filter XML element (see Section 10.5)
in the REPORT request only make reference to properties and
parameters for which queries are supported by the server. i.e., if
the CARDDAV:filter element attempts to reference an unsupported
property or parameter, this precondition is violated. Servers
SHOULD report the CARDDAV:prop-filter or CARDDAV:param-filter for
which it does not provide support.
<!ELEMENT supported-filter (prop-filter*,
param-filter*)>
(CARDDAV:supported-collation): Any XML attribute specifying a
collation MUST specify a collation supported by the server as
described in Section 8.3.
Postconditions:
(DAV:number-of-matches-within-limits): The number of matching
address object resources must fall within server-specific,
predefined limits. For example, this condition might be triggered
if a search specification would cause the return of an extremely
large number of responses.
8.6.1. Example: Partial retrieval of vCards matching a NICKNAME
In this example, the client requests the server to search for address
object resources that contain a NICKNAME property whose value equals
some specific text, and to return specific vCard properties for those
vCards found. In addition the DAV:getetag property is also requested
and returned as part of the response.
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Internet-Draft vCard Extensions to WebDAV (CardDAV) February 20088.7. CARDDAV:addressbook-multiget Report
The CARDDAV:addressbook-multiget REPORT is used to retrieve specific
address object resources from within a collection, if the Request-URI
is a collection, or to retrieve a specific address object resource,
if the Request-URI is a address object resource. This report is
similar to the CARDDAV:addressbook-query REPORT (see Section 8.6),
except that it takes a list of DAV:href elements instead of a
CARDDAV:filter element to determine which address object resources to
return.
Support for the addressbook-multiget REPORT is REQUIRED.
Marshalling:
The request body MUST be a CARDDAV:addressbook-multiget XML
element (see Section 10.6, which MUST contain at least one DAV:
href XML element, and one optional CARDDAV:address-data element as
defined in Section 10.4. If the Request-URI is a collection
resource, then the DAV:href elements MUST refer to resources
within that collection, and they MAY refer to resources at any
depth within the collection. As a result the "Depth" header MUST
be ignored by the server and SHOULD NOT be sent by the client. If
the Request-URI refers to a non-collection resource, then there
MUST be a single DAV:href element that is equivalent to the
Request-URI.
The response body for a successful request MUST be a DAV:
multistatus XML element.
The response body for a successful CARDDAV:addressbook-multiget
REPORT request MUST contain a DAV:response element for each
address object resource referenced by the provided set of DAV:href
elements. Address data is returned in the CARDDAV:address-data
element inside the DAV:prop element.
In the case of an error accessing any of the provided DAV:href
resources, the server MUST return the appropriate error status
code in the DAV:status element of the corresponding DAV:response
element.
Preconditions:
(CARDAV:supported-address-data): The attributes "content-type" and
"version" of the CARDDAV:address-data XML elements (see
Section 10.4) specify a media type supported by the server for
address object resources.
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However, if a client needs to make a change to a vCard, it can only
change the entire vCard data via a PUT request. There is no way to
incrementally make a change to a set of properties within a vCard
object resource. As a result the client will have to cache the
entire set of properties on a resource that is being changed.
9.2. Use of Locking
WebDAV locks can be used to prevent two clients modifying the same
resource from either overwriting each others' changes (though that
problem can also be solved by using ETags) and also to prevent the
user from making changes that will conflict with another set of
changes. In a multi-user address book system, the address book
client could lock an address object resource while the user is
editing the vCard data, and unlock the address object resource when
the user finishes or cancels. Locks can also be used to prevent
changes while data is being reorganized. For example, an address
book client might lock two address book collections prior to moving a
bunch of address object resources from one to another.
Clients may request a lock timeout period that is appropriate to the
use case. When the user explicitly decides to reserve a resource and
prevent other changes, a long timeout might be appropriate, but in
cases when the client automatically decides to lock the resource the
timeout should be short (and the client can always refresh the lock
should it need to). A short lock timeout means that if the client is
unable to remove the lock, the other address book users aren't
prevented from making changes.
9.3. Finding address books
Much of the time an address book client (or agent) will discover a
new address book's location by being provided directly with the URL.
E.g. a user will type his or her own address book location into
client configuration information, or cut and paste a URL from email
into the address book application. The client need only confirm that
the URL points to a resource which is an address book. The client
may also be able to browse WebDAV collections to find address book
collections.
The choice of HTTP URLs means that address object resources are
backward compatible with existing software, but does have the
disadvantage that existing software does not usually know to look at
the OPTIONS response to that URL to determine what can be done with
it. This is somewhat of a barrier for WebDAV usage as well as with
CardDAV usage. This specification does not offer a way through this
other than making the information available in the OPTIONS response
should this be requested.
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For address book sharing use cases, one might wish to find the
address book belonging to another user. If the other user has an
address book in the same repository, that address book can be found
by using the principal namespace required by WebDAV ACL support.
Because CardDAV requires servers to support WebDAV ACL [RFC3744]
including principal namespaces, and with the addition of the CARDDAV:
addressbook-home-set property, there are a couple options for CardDAV
clients to find one's own address book or another user's address
book.
In this case, a DAV:principal-match REPORT is used to find a named
property (the CARDDAV:addressbook-home-set) on the Principal-URL of
the current user. Using this, a WebDAV client can learn "who am I"
and "where are my address books". The REPORT request body looks like
this:
<?xml version="1.0" encoding="utf-8" ?>
<D:principal-match xmlns:D="DAV:">
<D:self/>
<D:prop>
<C:addressbook-home-set
xmlns:C="urn:ietf:params:xml:ns:carddav"/>
</D:prop>
</D:principal-match>
To find other users' address books, the DAV:principal-property-search
REPORT can be used to filter on some properties and return others.
To search for an address book owned by a user named "Laurie", the
REPORT request body would look like this:
<?xml version="1.0" encoding="utf-8" ?>
<D:principal-property-search xmlns:D="DAV:">
<D:property-search>
<D:prop>
<D:displayname/>
</D:prop>
<D:match>Laurie</D:match>
</D:property-search>
<D:prop>
<C:addressbook-home-set
xmlns:C="urn:ietf:params:xml:ns:carddav"/>
<D:displayname/>
</D:prop>
</D:principal-property-search>
The server performs a case-sensitive or caseless search for a
matching string subset of "Laurie" within the DAV:displayname
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Description: See Section 8.6.
Definition:
<!ELEMENT addressbook-query ((DAV:allprop |
DAV:propname |
DAV:prop)?, filter)>
10.4. CARDDAV:address-data XML Element
Name: address-data
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Specifies one of the following:
1. A supported media type for address object resources when
nested in the CARDDAV:supported-address-data property;
2. The parts of an address object resource should be returned by
a given address book REPORT;
3. The content of an address object resource in a response to an
address book REPORT.
Description: When nested in the CARDDAV:supported-address-data
property, the CARDDAV:address-data XML element specifies a media
type supported by the CardDAV server for address object resources.
When used in an address book REPORT request, the CARDDAV:address-
data XML element specifies which parts of address object resources
need to be returned in the response. If the CARDDAV:address-data
XML element doesn't contain any CARDDAV:prop elements, address
object resources will be returned in their entirety.
Finally, when used in an address book REPORT response, the
CARDDAV:address-data XML element specifies the content of a
address object resource. Given that XML parsers normalize the
two-character sequence CRLF (US-ASCII decimal 13 and US-ASCII
decimal 10) to a single LF character (US-ASCII decimal 10), the CR
character (US-ASCII decimal 13) MAY be omitted in address object
resources specified in the CARDDAV:address-data XML element.
Furthermore, address object resources specified in the CARDDAV:
address-data XML element MAY be invalid per their media type
specification if the CARDAV:address-data XML element part of the
address book REPORT request did not specify required properties
(e.g., UID, etc.) or specified a CARDDAV:prop XML element with the
"novalue" attribute set to "yes".
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Note: The CARDDAV:address-data XML element is specified in requests
and responses inside the DAV:prop XML element as if it were a
WebDAV property. However, the CARDDAV:address-data XML element is
not a WebDAV property and as such it is not returned in PROPFIND
responses nor used in PROPPATCH requests.
Note: The address data embedded within the CARDDAV:address-data XML
element MUST follow the standard XML character data encoding
rules, including use of &lt;, &gt;, &amp; etc entity encoding or
the use of a <![CDATA[ ... ]]> construct. In the later case the
vCard data cannot contain the character sequence "]]>" which is
the end delimiter for the CDATA section.
Definition:
<!ELEMENT address-data EMPTY>
when nested in the CARDDAV:supported-address-data property
to specify a supported media type for address object
resources;
<!ELEMENT address-data (allprop | prop*)>
when nested in the DAV:prop XML element in an addressbook
REPORT request to specify which parts of address object
resources should be returned in the response;
<!ELEMENT address-data (#PCDATA)>
<!-- PCDATA value: address data -->
when nested in the DAV:prop XML element in an addressbook
REPORT response to specify the content of a returned
address object resource.
<!ATTLIST address-data content-type CDATA "text/vcard"
version CDATA "3.0">
<!-- content-type value: a MIME media type -->
<!-- version value: a version string -->
attributes can be used on all three variants of the
CALDAV:address-data XML element.
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Name: allprop
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Specifies that all properties shall be returned.
Description: This element can be used when the client wants all
properties of components returned by a report.
Definition:
<!ELEMENT allprop EMPTY>
NOTE: The CARDDAV:allprop element defined here has the same name as
the DAV:allprop element defined in WebDAV. However, the CARDDAV:
allprop element defined here uses the
"urn:ietf:params:xml:ns:carddav" namespace, as opposed to the "DAV:"
namespace used for the DAV:allprop element defined in WebDAV.
10.4.2. CARDDAV:prop XML Element
Name: prop
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Defines which properties to return in the response.
Description: The "name" attribute specifies the name of the
addressbook property to return (e.g., "NICKNAME"). The "novalue"
attribute can be used by clients to request that the actual value
of the property not be returned (if the "novalue" attribute is set
to "yes"). In that case the server will return just the vCard
property name and any vCard parameters and a trailing ":" without
the subsequent value data.
Definition:
<!ELEMENT prop EMPTY>
<!ATTLIST prop name CDATA #REQUIRED
novalue (yes | no) "no">
<!-- name value: a vCard property name -->
<!-- novalue value: "yes" or "no" -->
NOTE: The CARDDAV:prop element defined here has the same name as the
DAV:prop element defined in WebDAV. However, the CARDDAV:prop
element defined here uses the "urn:ietf:params:xml:ns:carddav"
namespace, as opposed to the "DAV:" namespace used for the DAV:prop
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element defined in WebDAV.
10.5. CARDDAV:filter XML Element
Name: filter
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Determines which matching objects are returned.
Description: The "filter" element specifies the search filter used
to match address objects that should be returned by a report.
Definition:
<!ELEMENT filter (prop-filter*)>
10.5.1. CARDDAV:prop-filter XML Element
Name: prop-filter
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Limits the search to specific properties.
Description: The CARDDAV:prop-filter XML element specifies a search
criteria on a specific vCard property (e.g., NICKNAME). An
address object is said to match a CARDDAV:prop-filter if:
* A property of the type specified by the "name" attribute
exists, and the CARDDAV:prop-filter is empty, or it matches the
CARDDAV:text-match conditions if specified, and that any
CARDDAV:param-filter child elements also match.
or:
* A property of the type specified by the "name" attribute does
not exist, and the CARDAV:is-not-defined element is specified.
Definition:
<!ELEMENT prop-filter (is-not-defined |
(text-match?, param-filter*))>
<!ATTLIST prop-filter name CDATA #REQUIRED>
<!-- name value: a vCard property name (e.g., "NICKNAME") -->
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Name: param-filter
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Limits the search to specific parameter values.
Description: The CARDDAV:param-filter XML element specifies a search
criteria on a specific vCard property parameter (e.g., TYPE) in
the scope of a given CARDDAV:prop-filter. A vCard property is
said to match a CARDDAV:param-filter if:
* A parameter of the type specified by the "name" attribute
exists, and the CARDDAV:param-filter is empty, or it matches
the CARDDAV:text-match conditions if specified.
or:
* A parameter of the type specified by the "name" attribute does
not exist, and the CARDDAV:is-not-defined element is specified.
Definition:
<!ELEMENT param-filter (is-not-defined | text-match)?>
<!ATTLIST param-filter name CDATA #REQUIRED>
<!-- name value: a property parameter name (e.g., "TYPE") -->
10.5.3. CARDDAV:is-not-defined XML Element
Name: is-not-defined
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Specifies that a match should occur if the enclosing
property or parameter does not exist.
Description: The CARDDAV:is-not-defined XML element specifies that a
match occurs if the enclosing property or parameter value
specified in an address book REPORT request does not exist in the
address data being tested.
Definition:
<!ELEMENT is-not-defined EMPTY>
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Name: text-match
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: Specifies a substring match on a property or parameter
value.
Description: The CARDDAV:text-match XML element specifies text used
for a substring match against the property or parameter value
specified in an address book REPORT request.
The "collation" attribute is used to select the collation that the
server MUST use for character string matching. In the absence of
this attribute the server MUST use the "i;unicode-casemap"
collation.
The "negate-condition" attribute is used to indicate that this
test returns a match if the text matches, when the attribute value
is set to "no", or return a match if the text does not match, if
the attribute value is set to "yes". For example, this can be
used to match components with a CATEGORIES property not set to
PERSON.
The "match-type" attribute is used to indicate the type of match
operation to use. Possible choices are:
"equals" - an exact match to the target string
"contains" - a substring match, matching anywhere within the
target string
"starts-with" - a substring match, matching only at the start
of the target string
"ends-with" - a substring match, matching only at the end of
the target string
Definition:
<!ELEMENT text-match (#PCDATA)>
<!-- PCDATA value: string -->
<!ATTLIST text-match
collation CDATA "i;unicode-casemap"
negate-condition (yes | no) "no"
match-type (equals|contains|starts-with|ends-with) "contains">
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Internet-Draft vCard Extensions to WebDAV (CardDAV) February 200810.6. CARDDAV:addressbook-multiget XML Element
Name: addressbook-multiget
Namespace: urn:ietf:params:xml:ns:carddav
Purpose: CardDAV report used to retrieve specific address objects
via their URIs.
Description: See Section 8.7.
Definition:
<!ELEMENT addressbook-multiget ((DAV:allprop |
DAV:propname |
DAV:prop)?,
DAV:href+)>
11. Internationalization Considerations
CardDAV allows internationalized strings to be stored and retrieved
for the description of address book collections (see Section 6.2.1).
The CARDDAV:addressbook-query report (Section 8.6) includes a text
searching option controlled by the CARDDAV:text-match element and
details of character handling are covered in the description of that
element (see Section 10.5.4).
12. Security Considerations
HTTP protocol transactions are sent in the clear over the network
unless protection from snooping is negotiated. This can be
accomplished by use of TLS as defined in [RFC2818]. In particular,
if HTTP Basic authentication is available, the server MUST allow TLS
to be used at the same time, and SHOULD prevent use of Basic
authentication when TLS is not in use.
With the ACL extension present, WebDAV allows control over who can
access (read or write) any resource on the WebDAV server. In
addition, WebDAV ACL provides for an "inheritance" mechanism, whereby
resources may inherit access privileges from other resources. Often
the "other" resource is a parent collection of the resource itself.
Clients MUST take care to ensure users are aware of which address
books may be "private" (i.e. only accessible to them) and which are
"shared" (i.e. accessible to others).
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Since webservers are often the target of automated indexing
applications that gather data from the server, analyze it and extract
'interesting' parts, great care must be taken when allowing
unauthenticated access to any address book or address object data.
Clients MAY choose to warn users when they create address data in a
public address book, copy or move address data into public address
books, or change access privileges in such a way as to expose address
data to unauthenticated users.
This specification currently relies on standard HTTP authentication
mechanisms for identifying users. These comprise Basic and Digest
authentication as well as SSL using client-side certificates.
13. IANA Consideration
In addition to the namespaces defined by RFC4918 [RFC4918] for XML
elements, this document uses a URN to describe a new XML namespace
conforming to a registry mechanism described in RFC3688 [RFC3688].
All other IANA considerations mentioned in RFC4918 [RFC4918] also
apply to this document.
13.1. Namespace Registration
Registration request for the carddav namespace:
URI: urn:ietf:params:xml:ns:carddav
Registrant Contact: See the "Author's Address" section of this
document.
XML: None. Namespace URIs do not represent an XML specification.
14. Acknowledgments
Thanks go to Lisa Dusseault and Bernard Desruisseaux for their work
on CalDAV, on which CardDAV is heavily based. The following
individuals contributed their ideas and support for writing this
specification: Stefan Eissing, Arnaud Quillaud, Julian Reschke, Elias
Sinderson, Greg Stein, Wilfredo Sanchez Vega.
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Full Copyright Statement
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contained in BCP 78, and except as set forth therein, the authors
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